Apparatus for and method of milking an animal

ABSTRACT

Transducers are acted upon by milk flowing respectively from each teat of the animal into a milking claw which has an upper chamber and a lower chamber. The transducers respond to a condition of the milk and a processor controls valves. If the transducer indicates normal milk, the valve is set to direct flow into the lower chamber from which it passes via a pipe to a collection tank. If abnormal milk is indicated, the valve is set to direct flow into the upper chamber from which it passes via a discharge pipe to a dump container or drain. The transducers, the control valves and preferably also the processor are housed within the milking claw.

Benefit of priority is claimed of application Ser. No. 08/244,708, filedJun. 6, 1994, now U.S. Pat. No. 5,664,521, granted Sep. 9, 1997, ofwhich the present case is a continuation-in-part.

The invention relates to apparatus for and a method of milking an animaland is concerned with the automatic provision of information about theanimal during milking by monitoring the milk and detecting a monitoredcondition in the milk, if such condition arises.

An electrical measuring device is known from German patent specificationDE 1949559 for examination of milk during milking for pathologicalchanges, in particular changes indicative of mastitis infection.Measuring transducers, responding to the conductivity and/orpermeability and/or the dielectric constants of the milk, are arrangedto monitor milk originating from different teats of the animal beingmilked.

One problem is the provision of a reference standard because thementioned properties of the milk, even when normal, will vary from oneanimal to another, from one day to another and in dependence upon thefood the animal has been eating. The solution proposed by DE 1949559relies upon the observation that it is common for mastitis to affect, atleast initially, only one of the four teats of the udder. Accordingly DE1949559 arranges the four transducers in a bridge circuit, which goesunbalanced if the conductivity of the milk from one teat changes withrespect to that from the other three teats. There is, however, noindication of which teat is the source of milk of changed conductivity.DE 1949559 suggests it is possible to discover which teat is the sourceof milk of changed conductivity by substituting a resistor for eachconductivity cell in turn, the resistor having a resistance equal to theresistance of a conductivity cell when filled with uninfected milk. Suchan approach would be cumbersome in any event, but is impracticablebecause of the problem mentioned above in discovering the requiredreference standard for the value of the resistor on the day for theparticular animal.

European patent specifications EP 0 223 536 and 0 018 419 describe anapparatus for monitoring parameters such as electrical conductivity ofmilk during milking and separately for each milk flow line from theindividual teats of the animal. Neither of these patent specificationsconsider the possibility of automatic diversion of infected milk fromindividual teats. The problem of a reference standard is not addressedat all in EP 0 223 536. EP 0 018 419 proposes that the lowestconductivity reading be adopted as the reference. However this isunsatisfactory as it is not unusual for a healthy animal to produce ananomalously low reading from one teat.

European patent specification EP 0 385 539 discloses a conductivitymonitor for milk flow from each separate quarter and also separateautomatic diversion for each milk flow line in the event of mastitisdetection. Conductivity measurement is compared with a preset fixedvalue but some of the difficulties mentioned above which this presentsare recognised and a preferred approach proposed. This involves acomputer comparison based upon the spread of conductivities from theindividual quarters and/or development of a progressive averagedetermined over a number of days for the relevant cow. It is not,however, made clear how the spread of conductivities contributes to thedetermination, nor how an average built up over days is useful for themeasurement which has to be relevant for a particular day.

An appreciation on which the present invention is based, is the conceptof rapid automatic indication of which path is carrying milk from aninfected teat, and further, providing automatic control to divert theoutflow of such milk when detected. For realisation of these conceptsnew solutions have been devised for the provision of both a referencestandard and adequate detection sensitivity. More particularly thepresent invention is based upon an appreciation of the need to providesuch capabilities in an apparatus which a farmer can easily substitutewithin an existing milking plant.

In accordance with the present invention there is provided apparatus foruse in the milking of an animal which comprises a milking claw having aplurality of inlet paths, a common outlet path, a subsidiary outletpath, a respective transducer associated with each inlet path forproviding a quantitative signal representing the magnitude of a propertyof milk in that paths comparison means for comparing the said signal ineach inlet path with a reference, the comparison means providing anoutput signal which identifies the inlet path in which the milk has amagnitude of the said property differing by more than a predeterminedamount from the reference magnitude, and a diverter valve in each of thesaid inlet paths which diverter valve is operable to divert flow fromthe inlet path away from the said common outlet path to the saidsubsidiary outlet path, the said transducers, respective diverter valvesand portions of the inlet and outlet paths associated with the divertervalves all being contained within the milking claw.

In the context of the present specification the term "milking claw" isused in accordance with its recognised meaning to farmers. Essentially,a milking claw comprises a manifold unit, reasonably easily handled,from which extend flexible pipes to teat cups (typically four) toprovide milk flow paths from each teat cup via the manifold unit to acommon milk outlet path. Further flexible pipes from the manifold unitprovide the required vacuum pulsation to the teat cups. In use themilking claw must be such as can hang freely, suspended solely by itsvacuum attachment to the teats of the animal being milked.

Preferably control means responsive to the said output signal actuatethe valve in the input path identified by the output signal to divertflow to the said subsidiary outlet path. Preferably the comparison meansand the control means are also housed within the milking claw.Conveniently, the control means is so arranged that, during an initialstage of milking, the valves direct milk from all the inlet paths to thesubsidiary outlet path and, at the end of the initial stage, some or allof the valves are operated to direct milk from the corresponding inletpaths to the said common outlet path.

The said reference magnitude is preferably derived by reference meansduring milking from the magnitudes of the said property of the milk inthe said plurality of inlet paths, conveniently as an average of thesignals representing the respective magnitudes of the property of themilk in the inlet paths. In a preferred arrangement the reference meansderive the said reference, with which the signal from any one inlet pathis compared, as an average of the signals representing the respectivemagnitudes of the property of the milk in all of the other inlet paths.

The monitored condition may be the presence in the milk of a substancewhich is one of the group comprising progesterone, pheromone andsubstances resulting from the occurrence of mastitis in the animal or anabnormal concentration of such substance in the milk. The monitoredproperty may be electrical conductivity or some other property of themilk and the indication may be provided when the value of the propertyfalls below or exceeds a threshold value.

The milk may be monitored by determining the effect of the milk onenergy applied to the milk. The energy may be electromagnetic energy,alternatively, the milk may be monitored by monitoring the value of anelectrical property of a device which is exposed to the milk or tosubstances from the milk.

The milk may be monitored by means of a known technique for detectingthe presence of specific, organic substances.

Preferably, the milk is monitored continually during at least asubstantial part of the milking process.

Specific constructions of apparatus embodying the invention will now bedescribed by way of example and with reference to the drawings filedherewith, wherein:

FIG. 1 is a perspective view of a milking claw,

FIG. 2 is a cross-section through the claw of FIG. 1,

FIG. 3 is a diagrammatic representation of a known arrangement forillustrating the principle of operation of an electrical detectionapparatus,

FIG. 3a is a representation of the equivalent electrical circuit of FIG.3,

FIG. 4 is a part sectional view of another milking claw containing anelectrical detection apparatus,

FIG. 5 is a circuit diagram of part of the electronic circuitry of theapparatus,

FIG. 6 is a circuit diagram of another part of the electronic circuitry,

FIG. 7 is a circuit diagram of a further part of the electroniccircuitry,

FIG. 8 is a part-sectional diagrammatic representation of a modificationof the milking claw of FIG. 4.

FIG. 1 shows that part of a milking machine which is referred to as the"claw" and is suitable for use in the milking of a cow having an udderwith four teats. The claw has tubes 110 to 113 which lead to known teatcups (not shown) which are applied to the teats of a cow for milking.The tubes 110 to 113 lead via respective transducers 114 to 117 to ahollow housing 118 which is divided into upper and lower chambers 119and 120 by a partition 121.

A main pipe 122 leads from the chamber 120, via a transducer 123, to amilk treatment device, for example a cooler, and a milk storage tank. Apipe 124 leads from the chamber 119 via a transducer 125 to a dumpbucket (not shown) or a drain. Pulse tubes are omitted from the drawingfor clarity but may be arranged in known manner.

Inside the housing 118, the tube 110 divides into branches 126 and 127which lead respectively into the chambers 119 and 120. A valve 128represented diagrammatically in FIG. 2 is provided to direct milkentering the housing 118 along the tube 110 into either the branch 126or the branch 127. An electrically energisable actuator (not shown) isprovided for moving the valve 128 to a selected position. Each of thetubes 111, 112 and 113 is provided with branches corresponding to thebranches 126 and 127 and with a valve corresponding to the valve 128.

The transducer 114 is adapted for applying energy to the milk and meansis provided for monitoring the effect of the milk on the applied energy.The transducer 114 may be a known device for applying electromagneticenergy to the milk which flows along the tube 110 and known means forresponding to the effect of the milk on the applied energy. Theoperation of the transducer 114 may be based on a known technique fordetecting the presence of specific, organic substances. The transducer114 may be other than a transducer for applying energy to the milk. Thetransducer 114 may be an electrical device, a property of which isaffected by one or more specific substances which may be present in themilk. For example, the device may be an ion sensitive field effecttransistor. Alternatively, the device may be arranged for carrying outchromatographic analysis of the milk. The passage for flow of milk pastthe transducer may be arranged to exclude air bubbles from a part of thepassage in the vicinity of the transducer.

The transducers 115, 116 and 117 may be identical with the transducer114. The transducers 123 and 125 may differ from the transducers 114 to117 but each may be one of the kinds of devices mentioned above. Thetransducers 123 and 125 may be adapted for determining the presence ofone or more specific substances whilst the transducers 114 to 117 areadapted for detecting the presence of one or more different substances.However, in an arrangement in which each of the transducers 114 to 117is capable of detecting the presence of each substance which is to bemonitored in the milk, then the transducers 123 and 125 may be omitted.

The transducers 114 to 117, 123 and 125, or some of these transducers,are connected with a processor (not shown) for processing signalsprovided by the transducers. The processor may be incorporated in thehousing 118. This is particularly advantageous, since it means that theclaw can readily be substituted for a conventional claw, the onlymodification which the farmer would then have to make to his existingsystem would be the connection of a suitable electrical power supply forthe operation of the processor and the diverter valves. As analternative the processor may be at a central station remote from thehousing. In the latter case, the processor is preferably arranged toprocess signals received from a number of claws identical to or similarto the claw of FIGS. 1 and 2. The central station may include one ormore indicators, for example a device providing a visual indication ofan abnormal or seasoned condition, and preferably includes means forrecording information derived from the several claws. Such aconfiguration does however, require that electrical connection leads arerequired for transmitting signals between the claw and the centralstation.

In this example the apparatus of FIGS. 1 and 2 is used in the milking ofa cow. Initially, the valves are set to divert milk from each teat intothe chamber 119, during an initial stage of milking, which may last foronly a few seconds, the fore milk is discarded. Also, during thisinitial stage of milking, the milk from each teat is monitored by thetransducers 114 to 117 for the presence of substances which are producedby mastitis in the udder of the cow. If no such substances are detected,then, after the initial stage of milking, the valves are operated todivert the milk from all of the teats into the chamber 120, from whichit flows to the storage tank.

If, during the initial stage of milking, the presence in the milk fromone teat of a substance which results from mastitis of the udder isdetected, then the milk from that teat is not diverted to the chamber120, but continues to flow to the chamber 119, from which it isdiscarded. Milk which is contaminated by the occurrence of mastitis inthe cow is thus prevented from reaching the chamber 20 and the milkstorage tank.

It is possible for the monitoring to be carried out only during theinitial stage of milking and the valves then set, according to theresult, for the duration of the milking of the particular animal on thatoccasion. We have now found it is preferable for the apparatus to be setto continue to monitor for the duration of the milking process.

One property of milk which is affected by the presence of a substanceresulting from mastitis is the electrical conductivity. Thus, in aparticular example, the transducers 114 to 117 may be transducers whichprovide an electrical signal which represents the electricalconductivity of the milk. The signals from the transducers 114 to 117can be compared electronically to provide a comparison of the electricalconductivity of the milk from each teat. An output from the electroniccomparison can be used to provide automatic control of actuation of thevalves 128.

Additionally, manually operable or remotely operable means may beprovided for controlling actuation of the valves 128 and this mayover-ride automatic control. Provision is made for resetting the valvesafter manual operation.

In another embodiment, the transducers 114 to 117 may be adapted toprovide signals representing the concentration of ions, for examplepotassium ions, sodium ions or hydrogen ions, or to provide a signalindicating the concentration of nagase in the milk.

In another embodiment transducers 114 to 117 are adapted for providingsignals which indicate the presence of or the concentrations of othersubstances in the milk, for example progesterone and pheromone. Thepresence of these substances in the milk provides an importantindication about the condition of the cow and comparison of theconcentrations in the milk from different teats may not provideadditional useful information. Thus, such a transducer provided at 123or 125 could be used to obtain this information.

FIGS. 3 to 7 illustrate an apparatus embodying the invention in whichelectrical conductivity of milk is monitored so as to provide anindication of the presence of a substance resulting from mastitis.

FIG. 3 illustrates the known principle upon which the electricaldetection apparatus of this example is based. Two toroidally wound coilscomprise windings on a former which may best be visualised as arectangular section straight rod on which windings extend from one endto the other, and the rod is then bent so that its ends join and itsaxis (the continuous axis) forms a circle. A medium 11, whose electricalconductivity is to be measured, is arranged to form a conductive loopthreading the two coils which provide respectively a drive coil 12 and adetection coil 13.

If the drive coil 12 is excited with an alternating electrical current,the conducting loop 11 of the test medium will provide coupling bytransformer action with the detection coil 13. The degree of couplingbetween the drive coil 12 and the detection coil 13 is dependent uponthe conductivity of the conducting loop 11. A measure of thisconductivity can thus be derived from measurement of the current inducedin the detection coil 13.

Whilst, in principle, the magnetic field produced by toroidally woundcoils is wholly contained within the toroid, precautions must be takento ensure that there is no coupling, or substantially no couplingbetween the drive coil and the detection coil except that provided viathe loop of conductive medium 11.

FIG. 3a represents schematically the equivalent circuit of FIG. 3.

FIG. 4 shows the electrical detection apparatus incorporated in amilking claw which comprises an enclosure 14 which is generally circularin plan and divided into four quadrants to provide four independentchambers 15, one of which is shown fully in section in FIG. 4. Theenclosure 14 is formed from two separable components, a base plate 16and a cap 17.

Each of the four chambers 15 has an inlet pipe 18 and a removable outletpipe 19 for connection respectively to a tube which leads to a knownteat cup (not shown) to be applied to the teat of a cow for milking and,on the outlet side, to a tube leading to the milk collection tank.

Screw threaded into a hole in the base plate 16 in each chamber 15 is asensor 21 for detecting changes in the electrical conductivity of milkflowing through a chamber 15. The sensor 21 comprises a toroidally-wounddrive coil 22 and a substantially identically constructed detector coil23. The coils are wound on rectangular section formers 24 and thewindings extend around the full circumferential extent of the toroids.The coil windings are encapsulated in insulating material and fit withinappropriately toroidally shaped hollow copper cans 25, 26 which areelectrically connected to earth. The drive coil 22 is thus isolated fromthe detector coil 23. Each can has an open end 27, 28 and the cans 25,26 are assembled back-to-back so that the open ends 27 and 28 are remotefrom one another. In this example the copper cans 25 and 26 are spacedapart from one another and the whole assembly encapsulated in insulatingmaterial.

Electrical leads 29, 31 to the coils pass through sealed apertures inmounting boss 32.

In the operating position, the access opening of pipe 19 within thechamber 15 is above the level of the top of the sensor 21 so that whenmilk is flowing through the chamber 15, the sensor 21 will be completelysubmerged. The encapsulated coils are attached to the mounting boss 32on legs 33 so that there is space for the milk to form a closedelectrically conducting loop which threads both of the toroidally woundcoils 22, 23.

The principle of operation of the sensor is as described with referenceto FIGS. 3 and 3a. The construction employing the copper cans andencapsulating insulation provides for minimum direct coupling betweenthe drive coil 22 and the detection coil 23.

The electronic components and circuits for driving the sensor 21 anddetecting the output signals are illustrated in FIGS. 5 to 7.

Referring to FIG. 5, output from the detection coil 23 is connectedacross a tuning capacitor C1 to an operational amplifier OA1 providing again of approximately 100. Output from the operational amplifier OA1 isfed on line L1 to detection circuitry described further below, and online L2 to a circuit which controls the drive to the drive coil 22.

All of the operational amplifiers shown in FIGS. 5 to 7 are provided, inconventional manner, with connections to a positive supply and anegative supply. These connections have been omitted from the diagramsto avoid unnecessary complication. However, in FIG. 5 an inset labelledcircuit M1 illustrates the supply lines which, in this example, areprovided at +15 and -15 volts relative to the ground line. As indicated,it may be desirable to include smoothing capacitors in the supplycircuit. It will thus be appreciated that the operational amplifiers arecapable of providing an output which can vary between -15 volts and +15volts relative to the ground line.

The signal on line L2 is applied to operational amplifier OA2 set up asa high gain amplifier operating effectively as a switch. The output fromoperational amplifier OA2 is applied across Zener diodes Z1 and Z2connected back-to-back. The drive coil 22 together with its parallelconnected tuning capacitor C2 is connected across the back-to-back Zenerdiodes Z1 and Z2.

When switched on, any initial signal detected from the detection coil 23will be at the resonant frequency of this coil together with capacitorC1. Consequently the signal on line L2 will cause amplifier OA2 toswitch at this frequency. The Zener diodes Z1 and Z2 are thereforedriven alternately to breakdown and the output applied across the drivecoil 22 is a square wave of amplitude equal to twice the breakdownvoltage of the Zener diodes and frequency equal to the resonantfrequency of the detection coil 23. This circuit arrangement thusprovides that the frequency of the drive is held locked to the resonantfrequency of the tuned circuit formed by the detection coil 23 togetherwith the tuning capacitor C1 and will follow changes should there be anyas a consequence of changes in the operating conditions of the sensor21.

The voltage of the output signal from the detection coil 23 is dependentupon the coupling between the drive coil 22 and detection coil 23 whichis in turn dependent upon the conductivity of the milk. The outputvoltage from the detection coil 23 thus provides an indication ofconductivity. The sensitivity of this indication is at a maximum whenthe detection coil 23 is operating at resonance. However, when operatingin this way at resonance, any slight departure from the resonantfrequency will affect significantly the output voltage. It is thus ofcritical importance that the frequency of the drive is held at theresonance frequency of the detection coil circuit. In this context, itis preferable for the resonant frequency of the resonant circuit formedby the drive coil 22 and tuning capacitor C2 to match that of thedetection coil 23 and tuning capacitor C1. However, this is not criticalsince the resonant frequency of the drive coil circuit affects theefficiency with which the drive signal is coupled but will not affectthe frequency of the drive signal.

Turning now to the detection circuitry, the signal on line L1 isconverted to a direct voltage, indicative of the conductivity of themilk, by a half wave rectifier comprising operational amplifier OA3 andassociated diodes D1 and D2, the direct negative feedback via diode D1effectively cutting off the negative half cycle.

The rectified signal is smoothed by the combination of resistor R3 andcapacitor C3 and the output buffered by operational amplifier OA4. FIG.6 shows the continuation of the circuit, with this output on line L3being combined at a summing point P with a voltage from operationalamplifier OA5, the value of which is adjustable by variable resistor VR1as a zero offset. A further operational amplifier OA6 with variableresistor VR2 in the feedback path provides for scale adjustment andfinal output from sensor 21 at point A1.

Each sensor in each of the quadrants of the claw 14 is provided withidentical electronic circuitry from detection coil to output A1. Thecorresponding outputs are shown on FIG. 6 labelled A2, A3, A4. These aresummed and an average generated by operational amplifier OA7 to providea reference output on line L4.

For each channel, a comparator OA8, as shown in FIG. 7, is provided andthe reference level on L4 compared with the output, shown for A1 in FIG.7. The comparator OA8 is set up so that lamp LP is illuminated when thesignal on Line A1 differs by more than a predetermined amount from thelevel on line L4.

For operation, the apparatus is initially set up with a liquid in eachof the chambers 15 having an electrical conductivity less than is likelyto be encountered in the test medium (milk). In each channel, variableresistor VR1 is adjusted to give a scale zero readout. The liquid ineach channel is then replaced with a liquid having a conductivity inexcess of the maximum expected. In each channel the variable resistorVR2 is adjusted to give a maximum scale deflection. After cleaning, theapparatus is then ready for operation on milk. The reference level on L4will represent the average conductivity of the milk passing through thefour chambers 15. If any one chamber 15 receives milk at a conductivitylevel differing significantly from the average, then the appropriatelamp LP(5) for that channel will light up.

It will be appreciated that alternatively, or additionally, an outputfrom comparator OA8 may be used to drive a control valve in the outletpipe 19 to divert milk away from the main collection tank in the eventthat the sensor in that chamber is indicating a level of conductivitydiffering from the average by more than a pre-determined amount.

FIG. 8 illustrates in diagrammatic form a modification of thearrangement shown in FIG. 4. Those components which are the same asthose shown in FIG. 4 carry the same reference numerals. The section hasbeen extended to show two of the four sensors 21 and two of the inletpipes 18.

In this modification, the claw has an upper chamber 15 and a lowerchamber 51. The upper chamber is not divided into separate quadrants,but each sensor 21 is positioned within a cylindrical pot 52. Each inletpipe 18 is positioned so as to be directly over the respective pot 52.An outlet pipe 53 leads from the upper chamber 15 to a dump bucket ordrain. The lower chamber 51 has an outlet pipe 54 leading to the milktreatment device and milk storage tank.

The support boss 32a of each transducer in this modification has acentral aperture 55 providing an outlet opening at the bottom of therespective pot 52. A valve 56 operated by a solenoid 57 is moveable bythe solenoid 57 between a closed position and an open position. In FIG.8, the valve 56 associated with the sensor 21 on the left of the figureis shown in the closed position, whilst the valve on the right hand sideof the figure is shown in the open position.

The solenoids 57 and also the integrated circuit electronics packagemarked IC are accommodated within a recess in the upper part of thechamber 51.

In operation of this modified apparatus, the valves 56 are all initiallyclosed and the first milk to arrive through each of the inlet pipes 18flows into and fills to overflowing the pots 52 containing the sensors21. Overflow milk escapes through the outlet pipe 53.

Conductivity measurement on the milk filling each pot 52 at this stageis carried out as described above with reference to FIGS. 4, 5, 6 and 7.If the measurement for any pot 52 indicates mastitis infection, then thevalve 56 for that particular pot is held closed for the duration of thatmilking session. All the milk from the associated teat is thus directedto the dump bucket or drain via pipe 53. When the flow from inlet pipe18 from that particular teat ceases, remaining milk in the pot 52 drainsslowly out through a small drain hole 58 at the bottom of the pot 52.

Where the test on the initial flow of milk into pot 52 shows normal, thevalve 56 is opened after the initial short period of time necessary forthe test, and the good milk flows into the lower chamber 51 and out tothe cooler and collection tank via pipe 54.

On completion of milking, all valves 56 are opened and cleaning iscarried out by backwashing via pipe 54.

The representation of the integrated circuits IC and the solenoids 57and associated linkages are highly diagrammatic. It will be appreciatedthat any suitable form of valve controlling outflow from the pots 52into the lower chamber 51 may be used. In particular, it is desirable toemploy a valve which can be opened wide to provide a clear and smoothflow path for both the milk flow and, after milking, for the backflowwashing.

The invention is not restricted to the details of the foregoingexamples. For instance, it is not essential to use zener diodes 21 and22 in the drive circuitry shown in FIG. 5. The amplifier OA2, operatingat high gain, is effectively switched at the natural resonance frequencyof the detector circuit. However, the operation of amplifier OA2 is moresatisfactory if the zener diodes are included.

Nor is it essential to provide two separate, grounded copper cans 25,26. An equivalent and effective unitary structure can be provided by apair of co-axial cylinders with a dividing wall extending across thespace between the cylinders perpendicularly to the axis and mid-waybetween the ends of the cylinders. The unitary structure can be madefrom any material of suitably high electrical conductivity.

With more sophisticated processing, it is possible to derive a rollingreference level from milk from three of the four quarters and thuscompare the signal from one quarter with this average from the otherthree.

We claim:
 1. Apparatus for use in the milking of an animal whichcomprises a milking claw having a plurality of inlet paths, a commonoutlet path, a subsidiary outlet path, a respective transducerassociated with each inlet path for providing a quantitative signalrepresenting the magnitude of a property of milk in that path,comparison means for comparing the said signal in each inlet path with areference, the comparison means providing an output signal whichidentifies the inlet path in which the milk has a magnitude of the saidproperty differing by more than a predetermined amount from thereference magnitude, and a diverter valve in each of the said inletpaths which diverter valve is operable to divert flow from the inletpath away from the said common outlet path to the said subsidary outletpath, the transducers, respective diverter valves and portions of theinlet and outlet paths associated with the diverter valves all beingcontained within the milking claw.
 2. Apparatus as claimed in claim 1,wherein control means responsive to the said output signal actuate thediverter valve in the input path identified by the output signal todivert flow to the said subsidiary outlet path.
 3. Apparatus as claimedin claim 2, wherein the comparison means and the control means are alsohoused within the milking claw.
 4. Apparatus as claimed in claim 2,wherein the control means operate the diverter valves, during an initialstage of milking to direct milk from all of the inlet paths to thesubsidiary outlet path and, at the end of the initial stage, operatesome or all of the valves to direct milk from the corresponding inletpaths to the said common outlet path.
 5. Apparatus as claimed in claim1, wherein reference means derive the said reference during milking fromthe magnitudes of the said property of the milk in the said plurality ofinlet paths.
 6. Apparatus as claimed in claim 5, wherein reference meansderive the said reference as an average of the signals representing therespective magnitudes of the property of the milk in the inlet paths. 7.Apparatus as claimed in claim 5, wherein the reference means derive thesaid reference, with which the signal from any one inlet path iscompared, as an average of the signals representing the respectivemagnitudes of the property of the milk in all of the other inlet paths.